Configure cobra using standard layout

This sets cobra up using the standard approach (the default when
running `cobra init`

It's then easier to run the app with commands such as:

`go run main.go run`

Signed-off-by: Luke Hinds <luke@redhat.com>

Makefile

@@ -14,7 +14,7 @@ LAYOUT_TMPL := ./certs/layout.tmpl
 
 build: modules
 	@mkdir -p bin
-	@go build -o ./bin/in-toto ./cmd/in-toto
+	@go build -o ./bin/in-toto ./cmd
 
 modules:
 	@go mod tidy

cmd/in-toto/completion.go → cmd/completion.go

@@ -1,4 +1,4 @@
-package main
+package cmd
 
 import (
 	"github.com/spf13/cobra"

cmd/in-toto/gendoc.go → cmd/gendoc.go

@@ -1,4 +1,4 @@
-package main
+package cmd
 
 import (
 	"github.com/spf13/cobra"

cmd/in-toto/key.go → cmd/key.go

@@ -1,4 +1,4 @@
-package main
+package cmd
 
 import (
 	"encoding/json"

cmd/in-toto/record.go → cmd/record.go

@@ -1,4 +1,4 @@
-package main
+package cmd
 
 import (
 	"fmt"

cmd/in-toto/root.go → cmd/root.go

@@ -1,4 +1,4 @@
-package main
+package cmd
 
 import (
 	"fmt"

cmd/in-toto/run.go → cmd/run.go

@@ -1,4 +1,4 @@
-package main
+package cmd
 
 import (
 	"fmt"

cmd/in-toto/sign.go → cmd/sign.go

@@ -1,4 +1,4 @@
-package main
+package cmd
 
 import (
 	"fmt"

cmd/in-toto/verify.go → cmd/verify.go

@@ -1,4 +1,4 @@
-package main
+package cmd
 
 import (
 	"fmt"

cmd/verify.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+
+set -e
+
+# Verify that generated Markdown docs are up-to-date.
+tmpdir=$(mktemp -d)
+go run ./cmd gendoc --dir "$tmpdir"
+echo "###########################################"
+echo "If diffs are found, run: go run ./cmd gendoc"
+echo "###########################################"
+diff -Naur "$tmpdir" doc/

main.go

@@ -0,0 +1,9 @@
+package main
+
+import (
+	"github.com/in-toto/in-toto-golang/cmd"
+)
+
+func main() {
+	cmd.Execute()
+}